1. Field of the Invention:
This invention relates to a multi-stage hydraulic machine. This invention also relates to a method for operating a multi-stage hydraulic machine.
2. Description of the Prior Art:
Recently pumping type power plants have been constructed at places where a high head can be obtained, so demand for multi-stage hydraulic machines, for example, multi-stage pump turbines, is increasing. Movable guide vanes are not provided in a conventional multi-stage pump turbine, so in order to operate it as a pump it must be started in water. However a multi-stage pump turbine with a large capacity needs a very high input power to start the multi-stage pump turbine as a pump in water. As a result of this, this starting method adversely effects the electric power system to which it is connected, and particularly adversely effects such system for an economical point of view. Moreover in the recently developed large capacity multi-stage hydraulic machines, condenser operation for rotating the runner in air and spinning reserve operation while the runner is rotating in air are required. In order to fill these requirements it is essential to start a multi-stage hydraulic machine in air as a pump under the condition where the water level is lowered such an amount that the runner is out of contact with the water.
However in a conventional multi-stage hydraulic machine, the structure of water flow path is so complicated that it was difficult to exhaust compressed air in each runner housing or chamber completely without exhaustion retardation. It was therefore difficult to start a multi-stage hydraulic machine in air as a pump, and accordingly condenser operation or spinning reserve operation were difficult.